This invention relates to attaching tabs onto layered metal battery components for tapping the battery-developed voltage and current.
The attachment to battery tabs of a connecting conductor is relatively easy where the tab metal is reasonably thick and it does not contact a layer of low melting point plastic. Resistance welding or laser welding provide comparatively easy solutions. For example, Morris used spot welding for his battery""s tabs (U.S. Pat. No. 5,585,206). Narukawa et al. used ordinary laser welding to both connect the tab collector to the casing and to seal the casing. The problem which this invention solves is the attachment of tabs to the conducting metal of the battery, such as in the battery of a co-pending U.S. patent application, Ser. No. 09/289,071, filed Apr. 8, 1999, now U.S. Pat. No. 6,280,873. In that battery, the metal conducting layers of the positive and negative electrodes are in the range of 0.3 to 3 xcexcm and adhere to a thin layer of polyimide which might be about 9 xcexcm thick. Consequently, extreme care is required, otherwise the polyimide plastic will melt leading to short circuits within the battery, and the conducting metal itself may also be damaged. Therefore, a small controlled amount of external energy must be used to effect the attachment or bonding.
The difficulties encountered with attaching tabs to very thin metal layer, e. g., a layer of gold from 0.3 xcexcm to 50 xcexcm thick are severe. Typically, in the uses envisioned for the thin metal layer, which is for a compact battery, a plastic sheet such as polyimide underlies the thin metal layer. Polyimide has a relatively low melting point. The thin polyimide substrate melts when resistance welding or ordinary laser welding is used. Ultrasonic welding doesn""t work because the sound wave energy is absorbed by the polyimide.
This invention solves the attachment problem by using wire bonding to attach a tab to the metal layer